1. Field of the Invention
The present invention relates to electric powered vehicles performing drive control and regenerative control using an electric motor.
2. Description of Related Art
There has been developed an electric powered vehicle running by transmitting a driving power or braking power generated by an electric motor to wheels. The driving power in such a vehicle is obtained by applying a predetermined voltage to the motor, while the braking power is obtained by using the electric motor as a load. The braking power is obtained, for example by using the electric motor as an electricity generator and converting the kinetic energy of a wheel into the electric energy, thereby imparting a torque in the opposite direction to the rotating direction to the motor (i.e. the torque works as a load). The control for obtaining the braking power using an electric motor as a load in such a manner is hereinafter referred to as regenerative control.
By performing such regenerative control, it is possible to supplement the braking power which cannot be sufficiently obtained mechanically with a conventional drum or disk brake. Also, this has an advantage of being able to retrieve the electric energy by storing the converted electric energy in a battery, as well as being able to supplement the braking power.
The electric powered vehicle with a function of the regenerative control has a usage state in which a user makes the electric powered vehicle run by performing the drive control (hereinafter referred to as “running state”), and a usage state in which a user makes the electric powered vehicle move by pushing it without performing the drive control or braking (hereinafter referred to as “pushed state”). For example, the pushed state is applied in the case where there is a need for moving the electric powered vehicle to a certain place in a parking space.
However, in the pushed state, since the pushing rotates a wheel of the electric powered vehicle, the electric motor connected to the wheel works as a electricity generator (a load), and therefore the regenerative control is performed, whereby the braking power works on the wheel. Thus, the user is subjected to a great load, and in the case where the user does not have enough strength, it is problematic because the electric powered vehicle cannot be moved.
Therefore, for the low velocity movement of the electric powered vehicle when pushed, there has been conventionally proposed a method for prohibiting the regenerative control at or below a predetermined velocity (which is above the pushing velocity, i.e. the velocity with which it is difficult to move the electric powered vehicle by pushing) so that a user who is pushing the electric powered vehicle is not subjected to a great load (See Japanese Patent Laid-Open No.2001-25101).
However, in the electric powered vehicle with the method described above applied thereto, since the regenerative control is prohibited at or below the predetermined velocity, the regenerative control is performed only at the velocity higher than the predetermined velocity. Accordingly, the regenerative control is prohibited even when a user wants to utilize the regenerative control at or below the predetermined velocity (for example, when the running velocity of the electric powered vehicle is decreased, or when a user wants to utilize the braking power by the regenerative control on a sloping road). This can cause a problem of a low regenerative efficiency because the regenerative energy cannot be retrieved at or below the predetermined velocity.